Sen. Marco Rubio (R) of Florida takes a reporter's question as a bipartisan group of senators announce that they have reached agreement on the principles of sweeping legislation to rewrite the nation's immigration laws, during a news conference at the Capitol in Washington, Monday.

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2016 is years away. But for Sen. Marco Rubio (R) of Florida, the next few weeks could prove to be critical to shaping his presidential prospects.

As one of four Republicans in the group of eight senators behind the bipartisan comprehensive immigration reform plan outlined Monday, as well as one of the party's most-buzzed-about potential White House contenders, Senator Rubio arguably has the most to gain – or lose – politically from the effort.

If the bill gets through, it could mark an important step in changing the GOP's image to one that's more inclusive and minority-friendly, potentially helping Rubio and his party win over more Hispanics in future elections. And it could cement Rubio's reputation as a bridge-builder – someone who has the trust of the party's conservative base and can bring it along, or at least neutralize some of its concerns, on a hot-button policy measure its members have historically opposed.

On the other hand, if the bill fails – or if it passes but winds up simply granting legal status to people here illegally without following through on the promise to secure the border – Rubio may find some of those same bridges burned. He would then face the delicate task of having to repair relations with the party's base, for whom illegal immigration has often proved a key voting issue in primaries.

In 2008, Republican Sen. John McCain of Arizona lost the Iowa caucuses badly in large part because of his support for the failed 2007 comprehensive immigration plan. During the most recent presidential election cycle, Texas Gov. Rick Perry drew fire from the right over his support for in-state college tuition for children of illegal immigrants. By contrast, Mitt Romney took a strong no-amnesty stand, famously calling for illegal immigrants to "self-deport." That may have helped Mr. Romney win the nomination, but he went on to garner just 27 percent of the Hispanic vote in the general election – a big reason for his loss to President Obama.

Rubio seems well aware of the potential pitfalls, and he has been careful to emphasize that he understands where those on the far right are coming from. He also isn't overpromising when it comes to what ultimately winds up in the bill (which has not yet been drafted), making clear that there's a chance he won't be able to support it in the end if, for example, adequate border-security triggers aren't included.

In an interview Tuesday with radio host Rush Limbaugh, Rubio said that if Mr. Obama tries to set off a "bidding war" by putting forward a proposal with more lenient provisions, "then there won't be a solution." He added: "I'm just trying to do the best I can with what's already a tough situation. I pray it works out. I can't guarantee that it will, but we're going to do our best."

For his part, Mr. Limbaugh – who has made clear that he opposes the plan, which he calls "amnesty" – was nevertheless complimentary of Rubio, telling him: "What you are doing is admirable and noteworthy," but adding that he doesn't trust the president on the matter.

The bill's prospects will likely hinge on timing as much as anything else. Frustrated by recent electoral losses, Republicans have been openly discussing for months the need to moderate the party's hard-line stance on immigration. As Senator McCain put it bluntly Monday: "The Republican Party is losing the support of our Hispanic citizens. And we realize this is an issue in which we are in agreement with our Hispanic citizens."

In addition, the rate of illegal immigration has abated in recent years – a phenomenon most analysts credit to the weak US economy – and that slowdown may be taking some of the passion out of the opposition, at least as compared with the last time the issue came up during the Bush years.

Rubio himself has evolved on the issue, since he has previously argued in favor of a "piecemeal" approach rather than one comprehensive bill. As Mickey Kaus of The Daily Caller tweeted this week: "If a pol had Rubio's convenient policy shifts + weren't a) moving 2 Dem side + b) Latino, what would MSM call him? #opportunisticflipflopper."

But if Congress passes a comprehensive reform package, will anyone really remember or care about Rubio's previous positioning? We doubt it. And it will provide a big stake to the claim that he represents the future of the Republican Party.